In vitro effects of selenium and T-cell growth factor (TCGF) on natural killer (NK) cell function of lymphocytes from human peripheral blood

The trace mineral element selenium (Se) is a nutrient required in the diet of many species, including humans. Considerable epidemiologic data suggests that Se may also be an important dietary consideration in reducing the risk of certain cancers in humans. We investigated whether the antitumor effect of Se related to any capacity of Se to modulate natural host immune defense mechanisms. We observed that exogenous Se at physiologic concentrations from 1 to 5 x 10^-6 M did not influence spontaneous natural killer (NK) cell cytotoxic function as measured in vitro in 4-hr ⁵¹chromium-release assays against radiolabeled K562 erythroleukemia target cells. Supraphysiologic concentrations of Se (5 x 10^-5 M) inhibited NK cell function completely, but this inhibition was 1) spontaneously reversible within 18 hr of additional culture in the absence of exogenous Se, or 2) could be prevented altogether by coincubation of effector cells with soluble T-cell growth factor (TCGF) at 10% final concentration. There was no effect by Se on the K562 target cells themselves in the cytotoxicity assay. These data suggest that Se may be a significant, non-toxic modulator with which the cytolytic mechanism of human NK cells can be probed.